The present invention relates to a hitch control system for an agricultural vehicle.
It is known that hitch control systems which are responsive only to sensed draft force will not maintain a constant load on the engine. In fact, under certain conditions, such systems can even cause engine stalling. Therefore, it has been believed that tractor productivity and performance could be improved if the hitch is raised during overload conditions such as when the engine speed is lowered or "drooping". This concept is illustrated in U.S. Pat. No. 4,077,475 to Hino et al, issued Mar. 7, 1978. A more sophisticated hitch control system utilizing an engine speed input is described in U.S. patent application, Ser. No. 360,748, filed Mar. 22, 1982 and assigned to the assignee of this invention. Another hitch control system which is responsive to engine speed is described in copending U.S. patent application, Ser. No. 501,690, filed June 6, 1983 and also assigned to the assignee of this invention. All of these engine speed responsive systems require expensive and complicated electronic components and circuits and cannot easily be added to current production hitch systems.